FIELD WATER BALANCE AND SIMULATED WATER RELATIONS OF PRAIRIE AND OAK-HICKORY VEGETATION ON DECIDUOUS FOREST SOILS

Abstract

A steady-state model of atmosphere-soil-plant water relations, implementing both the combined energy balance, aerodynamic calculation of evapotranspiration and a 5-layer Darcy soil-water flow system, was used to simulate on a daily basis the water status and budget of experimental plots with either prairie grass or oak forest vegetation. A field water balance study provided independent estimates of evapotranspiration and drainage, based on measurements of soil water at several depths during the growing season. Oak forest and prairie grass vegetation in southern Wisconsin [USA] showed an average evapotranspiration rate of 2.0 cm3 cm-2 wk-1 from mid-June to early Oct. based on a water balance of the top 180 cm of soil. Simulation results were in close agreement with the field estimates, although differences in time distribution were shown, particularly for the prairie grass plots. Actual evapotranspiration was greater due to soil water uptake at depths below 180 cm. Soil water drainage was negligible during most of the growing season for vegetated plots whereas drainage from treatments without vegetation was slightly less than the precipitation received. Soil water content was generally lower on vegetated plots than on nonvegetated plots during the growing season. The model provided a means of evaluating some phenomena not measured in the field experiments. Simulations suggested that the oak vegetation was under water stress on more days during the growing season than the prairie grass.